Quinidine | 56-54-2

Quinidine is a pharmaceutical agent that acts as a class I antiarrhythmic agent (Ia) in the heart. It is a stereoisomer of quinine, originally derived from the bark of the cinchona tree. The drug causes increased action potential duration, and well as an prolonged QT interval.

Quinidine 56-54-2 MFCD00135581

like all other class I antiarrhythmic agents, quinidine primarily works by blocking the fast inward sodium current (INa). Quinidine's effect on INa is known as a use dependent block. This means that at higher heart rates, the block increases, while at lower heart rates the block decreases. The effect of blocking the fast inward sodium current causes the phase 0 depolarization of the cardiac action potential to decrease (decreased Vmax).

Quinidine also blocks the slowly inactivating tetrodotoxin-sensitive Na current, the slow inward calcium current (ICa), the rapid (IKr) and slow (IKs) components of the delayed potassium rectifier current, the inward potassium rectifier current (IKI), the ATP-sensitive potassium channel (IKATP) and Ito.
At micromolar concentrations, quinidine inhibits Na⁺/K⁺-ATPase by binding to the same receptor sites as the digitalis glycosides such as ouabain.

The effect of quinidine on the ion channels is to prolong the cardiac action potential, thereby prolonging the QT interval on the surface ECG.
Other ECG effects include a wide notched P wave, wide QRS complex, depressed ST segment, and U waves. These are the results of both slowed depolarization and repolarization.

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Quinidine affects the way that the heart beats.

Quinidine is used to help keep the heart beating normally in people with certain heart rhythm disorders.

Quinidine may also be used for purposes not listed in this medication guide.

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